1. Technical Field
The present invention relates to a method of manufacturing a semiconductor device.
2. Related Art
In association with dimensional shrinkage, increase in the degree of integration and increase in operation speed of semiconductor devices, there has been a growing demand on lower resistivity of silicides formed on the gate electrodes and source/drain (impurity-diffused layer) regions. The situation has therefore promoted adoption of a Ni-containing silicide film which contains NiSi, NiPtSi or the like.
On the other hand, the silicide film has also been required to ensure a large selectivity in the process of dry etching for forming contact plugs, in order to prevent penetration through the thin silicide film, and to keep a necessary thickness of side walls. The situation, however, makes it more difficult to concomitantly satisfy removal of the depositional substance produced in the process, and oxidative solubilization of the silicide.
As an exemplary method of forming contact holes in an insulating film formed on a silicide layer, Japanese Laid-Open Patent Publication No. 2007-234760 describes a technique as described below.
According to Japanese Laid-Open Patent Publication No. 2007-234760, a SiN film is formed as an etching stopper film on a silicide layer, and a silicon oxide film is formed thereon as an interlayer insulating film. A resist film having a predetermined pattern which contain openings, through which contact holes are formed, is then formed, the silicon oxide film is then selectively removed by dry etching using the resist film as a mask, and the resist film is removed typically by O2 plasma ashing. Thereafter, the SiN film as the etching stopper film is selectively removed, using the silicon oxide film as a mask. The contact holes are formed in this way. According to the method of forming the contact holes described in the Publication, since the ashing takes place while leaving the SiN film as the etching stopper film unremoved, so that silicide layer may be prevented from being directly exposed to the O2 plasma.
In the above-described tendency towards lower resistivity, adoption of the Ni-containing silicide layer, such as NiSi, as the silicide has raised an additional need of keeping a large selectivity in the process of etching of SiN film used as the higher etching stopper film, with respect to the Ni silicide layer. As a consequence, the SiN film has necessarily been etched under conditions more likely to produce depositional substance in order to ensure such large selectivity, so that the depositional substance has been more likely to produce at the bottoms of the contact holes. Cleaning for removing the depositional substance is now a matter of importance, after the contact holes are formed.
This sort of depositional substance has generally been removed by ashing, or by cleaning using a mixed solution of aqueous ammonia and aqueous hydrogen peroxide solution (occasionally referred to as ammonia/hydrogen peroxide solution, hereinafter), hydrofluoric acid solution, or a mixed solution of sulfuric acid and aqueous hydrogen peroxide solution (occasionally referred to as sulfuric acid/hydrogen peroxide solution, hereinafter).
Japanese Laid-Open Patent Publication No. 2007-234760 discloses a process of forming the contact holes, followed by acid cleaning using hydrofluoric acid or the like, and treatment using an alkaline chemical. The Publication also discloses RF etching of the surface of the silicide layer.
Japanese Laid-Open Patent Publication No. 2002-146574 discloses that active cathode water and active anode water may also be applicable also to cleaning which is carried out after the openings, allowing the silicide layer to expose therein, are formed by etching.
According to the Publication, aqueous electrolyte solution which composes the active cathode water and active anode water contains 1 to 30% by mass of ammonium hydroxide and 1 to 30% by mass of fluoride.
The present inventors have recognized as follows. The related arts disclosed in the above-described Publications have, however, been suffering from a problem in the aspect below.
In the related art described Japanese Laid-Open Patent Publication No. 2007-234760, removal of the depositional substance on the silicide layer is accompanied by oxidation typically using an acid-containing aqueous solution or by oxygen plasma treatment. In the related art described in Japanese Laid-Open Patent Publication No. 2002-146574, the cleaning using an aqueous electrolyte solution containing 1 to 30% by mass of ammonium hydroxide essentially needs a succeeding process of rinsing with water.
However, the silicide layer, in particular Ni silicide layer, is susceptible to oxidation even by such rinsing using water.
As described in the above, removal of the depositional substance on the silicide layer by the related arts have been associated with undesirable oxidation of the silicide layer.